Filters or standards can have different purposes within a company, from routine verification of UV-Vis Spectrophotometer s, comparison of various devices within the same company, periodic inspections or even performing internal calibrations.
Depending on the use of the equipment, companies may have filters calibrated for wavelength, optical density, transmittance, Spectrophotometer linearity, and stray light.
These filters can be solid or liquid. Solids are glass mounted in 1 cm Spectrophotometer cuvettes, while liquids are present in sealed 1 cm Spectrophotometer cuvettes.
Wavelength Calibration Filters
Filters used for wavelength scale calibration of Spectrophotometer s are filters with distinctly narrow absorption bands for different wavelengths. Common standards for these calibrations are holmium and samarium oxide filters.
Holmium oxide filters exhibit absorption peaks in the UV-visible range from 240nm to 650nm.
Dysprosium filters also exhibit absorbance peaks in the UV-Vis range from 380nm to 900nm.
We can also calibrate filters for infrared wavelengths from 800nm to 1800nm. Filters for Absorbance and Transmittance Calibration
Filters for Absorbance and Transmittance Calibration
Optical filters or standards used in photometer calibration are used to determine the accuracy of the absorbance and transmittance values measured by the Spectrophotometer .
These standards or filters are usually neutral density glass mounted in holders compatible with 1cm Spectrophotometer cuvettes. These standards exhibit different absorbance values or percent transmittance at different wavelengths. The combination or use of multiple filters allows for an understanding of the error or correction of the device at different points on the luminosity or absorbance and transmittance scale.
For the UV region, it is also common to use a solution of potassium dichromate. These reference materials have absorbance values at different defined wavelengths.
We can also calibrate filters in the infrared range from 780nm to 2500nm.
Filters for Linear Calibration
Linearity calibration filters are used to evaluate the accuracy of a Spectrophotometer in determining the absorbance of a solution based on concentration. For this, different standards with different concentrations can be used. Potassium dichromate solution is usually used as reference substance. Then, evaluate the response of the device in terms of absorbance or transmittance.
Stray Light Calibration Filters
These filters, or standards, can be used to assess whether the Detector is receiving light other than the desired wavelength. The device's Detector does not distinguish between light passing through the sample and light that could reach the device from other sources.
Filters for stray light evaluation are typically solutions in sealed 1 cm cuvettes for Spectrophotometer s. These filters have the property of absorbing all light at a specific wavelength, so if the Detector detects light, it means the source is not the sample, hence diffuse light.
These filters are usually solutions of NaI, KCl, etc.
